1. Field of the Invention
The present invention relates generally to an agricultural device for pruning plant growth, and specifically to a device for pruning grapes.
2. Background
Grapes have been grown by mankind for thousands of years, producing fresh fruit as well as preservable products such as raisins, wine and distilled spirits. Early vineyardists discovered that by removing a measured amount of seasonal growth during dormancy, a more predictable quantity of fruit would be produced during the following growing season. These pruned vines consistently bore more fruit, of higher quality, than vines that did not have this seasonal growth removed.
Pruning practices specific to vines producing fruit for the fresh market, (such as table grapes), are especially important because they allow growers to maintain the critical balance between foliar growth and fruit growth required to produce grapes of consistent yield and quality.
Traditionally, pruning is performed by hand crews working in the vines during the winter dormant season (December-February). Hand-pruning of smaller vineyards is still a common practice, but many modern vineyards have grown very large requiring many pruning crews to complete the process during the optimal pruning window. The high cost and uncertain supply of people to do this work has forced viticulturalists to seek more cost effective and reliable means of pruning their vines.
One proven method that reduces pruning time, lowers overall cost and increases field capacity, is a two-step process that utilizes a combination of powered machinery and hand labor. A typical system will include a mechanical pruner mounted on, and powered by, a field tractor that will carry it over or alongside the vine row. The device will employ some type of cutter(s) that can remove a portion of the seasonal growth (sometimes in excess of ninety percent). This rough pruning is the first step of the process and can typically remove a large portion of the seasonal growth. This allows the second step of the operation, hand pruning the vine to the desired shape and bud count. Because the pruning process removes the majority of canes, hand crews move through the field much more rapidly than in situations where no pruning has taken place. This “mechanically assisted” hand pruning is safer and less fatiguing to workers since hand crews are no longer required to pull canes through the trellis wires as they work their way through the field. This two step process requires fewer people and less time than employing a hand crew to prune all the seasonal growth down to the final finishing cut.
To date, attempts to produce machines for pruning vines trained to produce table grapes have not met with success. This lack of success has much to do with how table grapevines are trained. Most pruning machines are designed to work on vines that have been pruned and trained in a way that forces seasonal growth upwards within a vertical plane directly above the vine arms (cordons). With the trunk of the vine supported by a stake and with a multitude of wires running the full length of the vinerow, above and on either side of the cordons, seasonal growth is constrained within a vertical plane growing upwards from the vine's arms. Having the canes (the vine's seasonal growth) oriented in this manner allows the cutter blades of a pruner to pass through these vertically oriented canes and cut them. By using several blades aligned on a common shaft making simultaneous cuts along the length of the canes, long canes are reduced to small cane sections that fall away and through the training wires, leaving shorter canes protruding from the cordons that are later finish pruned by hand.
Table grapes present additional challenges in terms of pruning. Due to the table grape's unique growing requirements, its seasonal growth may be oriented horizontally, reaching upwards and outward, supported by horizontal arms and trellising wire. Creating this horizontal canopy of leaves maximizes the photosynthesis capacity of the vine and provides a shaded environment for the fruit growing beneath the canopy.
To mechanically prune vines trained using the horizontal training system employed with table grapes, a pruning machine should have the ability to 1) position the cane cutting portions of the machine along a horizontal plane, enabling them to cross-cut the canes laying on the trellis wires; 2) cut canes while allowing the trellis wires and their associated support arms to pass through the cutting devices without being damaged; and 3) allow the operator to effectively control cut location, machine height, and alignment down the vine row.
Many existing pruning devices use a cutting system that relies on multiple rotating and/or non-rotating blades to sever the canes at multiple locations to reduce the quantity of seasonal growth. Some such devices utilize saw blades rotating at high speed and protective disks that rotate at the tractor's ground speed, creating a non-moving (relative to the canes being cut) series of guides that hold and feed the canes through the rotating blades. Other devices use non-moving blades aligned vertically. Between each set of blades is a rotating disk with protruding fingers that push the vertical canes through the blades, severing the canes.
What is needed is a device for pruning table grapes that has the ability to pre-prune horizontally trained vines, has no high-speed components such as circular saw blades, and has reduced maintenance and parts costs.